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In summary this query is about exporting a track or tracks from Basecamp to a CSV file; the resulting list of Points are all one hour behind the real time during BST.

I do three or four long walks per week and download them from my GPSMAP 64ST each evening then store them in Basecamp. I also keep an analysis in Excel so it is easy to play about with the data.

If I am looking at any one walk in particular I use Basecamp export function and create a csv file to show me all the recorded points for that walk. When we are on Summer Time (BST) the time showing when opening the csv file in excel is exactly one hour earlier (presumably GMT) than the real time of the walk. The GPSMAP always has the correct time set, my pc has the correct time and they are identical so I wonder why this might be? Where is it getting GMT from?

As an aside I occasionally export a batch of walks to a gpx file for importing in to Mapsource (because mapsource produces a better format for my excel history; which is another story). When I do this the start time of the walk is always correct.

The satnav and computers all work in GMT. It is up to the device to convert the time to local time.

Possibly for evidence / legal reasons the records may be stored in original format, rather than the format displayed on the screen.

If you look at the logs after riding / driving, the speeds are recorded as being all over the place. 70 mph for one record, 50 moh a second later. And yet the display was showing a steady 59mph with no fluctuations.

This is because the satnav cannot actually tell how fast your are travelling at a fixed point in time. It is probably recording the speed calculated over the distance travelled in the last second. Not the average over the longer time span that the satnav displays.

I discovered this issue when I was using the gpx logs from my satnav to geotag my photos by matching the time. Made more complicated by the different time zones in uk, spain and portugal. Of course I wanted my camera to show local time, and that is what it recorded. The satnav recorded GMT.

But you're in the Uk, the problem will fix itself at the end of this month !